The present invention relates to a microcapsule-containing adhesive system and method of using the same wherein the microcapsules are filled with a solvent which is capable of rendering the adhesive adherent. More particularly, the present invention relates to an adhesive-system which can be used to seal a facsimile document in an envelope before it leaves the facsimile machine so that it cannot be read without evidencing tampering.
Facsimile machines are now used almost universally in business. With the widespread use of these machines, a need has arisen to transmit documents in a strictly confidential manner. Currently this is not generally possible unless the intended recipient of the confidential document personally monitors the facsimile machine and gathers the document immediately as it is received. It has been proposed to design facsimile machines in which the transmitted document is automatically inserted into a tamper-evident envelope before it exits the facsimile machine so that the facsimile machine attendant cannot see the document and it is not necessary to stand by the machine and wait for transmission of the document.
While envelopes which are sealed with tamper-evident adhesives (so called tamper-evident envelopes) are known, the adhesives used in conjunction with these envelopes have not been satisfactory for use in a facsimile machine. The adhesives used in tamper-evident envelopes are often covered with a release film which is removed by the user immediately prior to sealing the envelope. The removal of such a release film is difficult to perform within the design limitations of conventional facsimile machines.
Another class of known adhesives which is used on most common envelopes is soluble adhesives which requires a solvent to activate the adhesive and produce its tackiness. These adhesives are also unsuitable for use in facsimile machines because a means must be provided to wet the adhesive and the adherents must be set and joined with speed and precision immediately after the solvent has been applied and the adhesive activated.
Adhesive systems employing microcapsules have been disclosed in the patent literature. One known system comprises a curable adhesive which contains rupturable microcapsules filled with a curing agent. See for example U.S. Pat. No. 4,940,852 to M. Chernack. An adhesive system containing microcapsules is also shown in U.S. Pat. No. 4,925,517 to Charbonneau et al. In this system, two substrates are temporarily adhered together with an adhesive which contains microcapsules filled with a fragrant liquid. When the adherents are pulled apart, the microcapsules break, releasing the fragrance. A further example is seen in which an adhesive coating, including a latex carrier having solvent-filled microcapsules is coated on a threaded fastener such as a bolt. When these microcapsules rupture, the solvent cures the adhesive to secure the fastener.
One of the most critical problems which arises in designing an adhesive for use in a tamper-evident envelope for use in a facsimile machine is that the envelopes or the substrate from which they are formed must be stacked together and folded and assembled with the document within the fax machine. This requires that the adhesive be non-tacky and have a low coefficient of friction. If the adhesive is tacky, the envelopes will stick together while they are stacked in the machine. If the adhesive exhibits a high coefficient of friction, it will interfere with handling the envelope and feeding the envelope through the machine as one envelope will drag another envelope along or cause misfeeds within the fax machine. While cohesives (as hereafter defined) are not tacky, they often exhibit a coefficient of friction which results in misfeeds.
Therefore, it is an object of the present invention to provide an adhesive system which is non-tacky and exhibits a low coefficient of friction, and which can be rendered adherent to provide a seal which is tamper-evident.